It's definitely a little anticlimactic and unsatisfying, but I think the way it makes sense is timing. The defenders didn't get to choose the timing, Mordor attacked, and they just had to hold out as long as they could. Every life given bought a little more time, which eventually meant Aragorn and his ghost buddies were still saving a city when they arrived instead of taking back a pile of rubble

I also think that mouth of Sauron sequence is sort of weird for Aragorn's character. He just lops the guy's head off and says "He was probably lying, let's do this suicide mission anyways."

I feel like it could've worked, but it would've taken more than that sequence to make Aragorn's actions seem reasonable at that point